1. Field of the Invention
This invention pertains, in general, to lighting devices for keyswitch assemblies and keyboards, such as computer desktop, laptop, and notebook keyboards or "Internet-TV" keyboards. More specifically, the invention relates to backlighting for keyboards that originates from below the keys within the keyboard.
2. Related Art
For a long time, keyswitch assembly operators have desired lighted keyboards and keypads. For example, when an operator is working a computer keyboard and simultaneously viewing a computer monitor, low ambient light conditions may be preferred, in order to maximize contrast on the monitor screen. Also, for example, a portable computer operator may by necessity be in a low light environment, as when flying in an airplane or riding in a train at night.
In any event, there have been many attempts in the prior art to provide lighted keyboards and keypads. Still, many of these attempts have not been successful because they result in keyswitch assemblies that are not sufficiently lighted, or lighted in a glaring or distracting manner, or that are inconvenient, or expensive. Prior attempts at lighted keyboards have produced fragile systems that consume more power and produce more heat than is desirable.
Examples of lighted keyswitch assemblies are found in the patent literature. U.S. Pat. No. 5,801,345 (Mikula-Curtis et al., 1998) discloses LED's attached to the bottom of the printed circuit board (PCB) which emit light that travels up through holes in the PCB and into light pipes, each of which is received in a key cap to channel the light up through the interior of the key cap. Also, the Mikula-Curtis et al. system includes a backlighting system with an LED centered under a light dam and an indicia panel, that emits light up through the center of the area enclosed by the light dam to back-light the indicia panel.
U.S. Pat. No. 5,612,692 (Dugas et al., 1997) discloses a sealed, LED-lighted keyboard, in which the LEDs are disposed on the printed circuit board. The LEDs and circuit board are covered by a spacer board with openings for allowing electrical contact with the top surface of the circuit board and for allowing LED light to reach the upper layers of the system. These "upper layers" include a translucent sealing sheet membrane with domes, and keys above the domes. Thus, in Dugas, the keys are pushed down to force the domes down so that a conductive under-surface of the key may contact the circuit board. The LED light must travel up through the spacer board holes, through the center of each dome, up through the center of each key, and out the translucent number, letter, or other indicia on the top center of the key cap.
U.S. Pat. No. 5,034,602 (Garcia, et al., 1991) discloses a backlighting system in which a light emitter, such as an alpha/numeric LED or LCD, is disposed beneath the center of the key cap or adjacent to a beam splitter that redirects the light up through the central axis of the key cap.
U.S. Pat. No. 4,806,908 (Krupnik, 1989) discloses a system using electroluminescent (EL) strips that extend through registering openings that extend transversely through the stems of the key switches in the keyboard. The EL strips extend from key stem to key stem underneath an opaque, stationary retaining panel being between the keys, so that only the key cap is lit only by light that is emitted from the area of the EL strips inside the key stems (the "internal portion") and that travels up to the cap of the key. This light from the internal portion of the EL strip travels up through the center of the clear, transparent, or translucent body of the key stem and then to openings or translucent areas in the center of the otherwise opaque key cap. Because the EL strips run underneath the opaque retaining panel and through openings in the stems of a plurality of keys, the EL strips are also adapted to prevent withdrawal of the keys from the retaining panel.
Summarily, therefore, conventional backlighting techniques feature means for channeling/directing light directly up through the center of the key cap or of the area directly under the indicia panel to be lit. This approach purposely controls the light to travel along a specific central axis and then to radiate from the keyboard in a limited area of a single key cap or of a single indicia panel. This approach purposely controls and limits the light path, to prevent light from traveling from keyswitch to keyswitch or from shining from the inside of the keyswitch to the outside of the keyswitch.
What is still needed is a durable, economical and effective backlighting system for a desktop, laptop, notebook, or "Internet-TV" keyboard. What is needed is such a system that supplies appropriate levels of light in the appropriate areas of the keyboard for enhanced viewing in low/no light environments.